If UNIX is too yesterday, Linux is just old hat, and you want something more interesting to work with, you may want to check out ReactOS or Syllable. These are just two of the six operating systems covered in InformIT's article, "A Roundup of Free Operating Systems." Writer David Chisnall disclaims from the beginning that these may not be as useful as Linux or UNIX, but they're "much more fun."
ReactOS began nearly a decade ago, geared toward producing a Windows NT clone. One of its attractions, according to Chisnall:
Because ReactOS always aimed to be binary-compatible with Windows, a lot of device drivers can be used directly without modification. While they can't use any of the Microsoft-supplied drivers for generic hardware, one of the strengths of Windows is that there is a plethora of third-party driver support.
Though the operating system "hasn't been tested much on real hardware" -- it's still in alpha development -- it works well in "virtualized environments." It might be worth a look when Microsoft stops supporting Windows XP, he says.
Syllable came about as a fork from AtheOS, and one of its biggest strengths is that there is no legacy to support, Chisnall says.
This is a two-edged sword, because it means that there is no existing software library for Syllable. This is not as bad as it might seem; beneath the GUI, Syllable supports a large subset of POSIX, and so much non-GUI Free Software can be easily ported.
Other operating systems Chisnall discusses include Haiku, Contiki, MenuetOS and AROS.